There is no way to add additional button to select popup:
https://ionicframework.com/docs/v2/api/components/select/Select/ - you can just set text for buttons.
You should use AlertController for that - it allows you to create buttons. Here is a good example:
https://github.com/driftyco/ionic-preview-app/blob/master/src/pages/alerts/radio/pages.ts
let alert = this.alertCtrl.create();
alert.setTitle('Lightsaber color');
alert.addInput({
type: 'radio',
label: 'Blue',
value: 'blue',
checked: true
});
alert.addInput({
type: 'radio',
label: 'Green',
value: 'green'
});
alert.addButton('Cancel');
alert.addButton({
text: 'Ok',
handler: data => {
console.log('Radio data:', data);
this.testRadioOpen = false;
this.testRadioResult = data;
}
});
alert.present().then(() => {
this.testRadioOpen = true;
});
Unfortunately 3rd button will damage alert UI, so you need to create some css to fix it.